This invention relates to zoom lenses with greatly increased image angle, and more particularly to a zoom lens consisting of a movable front lens group having a negative focal length and a movable rear lens group having a positive focal length, the rear lens group having a diaphragm incorporated therein, and the front and rear lens groups being axially moved in differential relation to each other to vary the focal length of the entire lens system, which zoom lens has photographic capabilities extended toward the wide angle side while still preserving good stabilization of aberrations throughout the zooming range with limitation of the overall dimensions of the zoom lens to a minimum.
As shown in FIG. 1, a zoom system which may be conveniently considered as comprising a negative front lens I and a positive rear lens II, both of which are moved axially but in differential relation to each other to effect variation of the focal length of the overall lens system is, because of its being of inverted telephoto type, advantageous in providing an increased extent of image angle. As the maximum axial separation between the front and rear lenses I and II occurs at the wide angle setting for the maximum image angle, however, there is a disadvantage to this zoom system such that an increase in the diameter of the front lens I must be made for the extended range of image angle toward the maximum. This problem becomes serious in designing a zoom lens with a greatly increased image angle. If the provision for increasing the maximum image angle is forced to be compatible with severe limitation of the overall dimensions of the zoom lens to a minimum, the barrel type distortion at the wide angle setting is rapidly increased and its satisfactory correction is made difficult by any means.